This invention relates to geothermal heating and cooling, and is more particularly concerned with a closed system in which geothermal water is used for removing sensible heat from indoor air, and a desiccant wheel is employed for removing humidity. The invention is more specifically directed to a geothermal air conditioning system in which the air stream is split into first and second air streams or courses, for removing both heat and humidity.
Abundant cooling resources are available from the earth in the form of geothermal cooling, which does not require significant energy to obtain, and which does not result in discharge of waste heat into the atmosphere. Geothermal cooling can be obtained by circulating water (or another heat exchange medium) through pipes that run to and from one or more geothermal wells. Because the ground temperature is constantly cooler than the temperature required for indoor air, geothermal sensible cooling appears to be an attractive option. However, in most parts of the U.S., the temperature of geothermal water coming from the geothermal well is not cold enough for dehumidification or latent cooling. In New York State, the deep earth temperature ranges between 46° F. in the Adirondacks and St. Lawrence valley, in the north part of the state, and 54° F. in the New York City area, and averaging about 50° F. statewide. Most other northern states have similar ground temperature conditions. Geothermal cooling can be used for “free” cooling of air, but the water being circulated is not cold enough, by itself, for dehumidification. The dewpoint of indoor air at 80° F. dry-bulb temperature and 67° F. wet-bulb temperature is about 60° F. The water circulated to deep earth temperatures of 46° to 54° F. will not return to the surface cold enough to dehumidify air with a dewpoint of 60° F.
Desiccant dehumidification has been employed for many applications, relying on indoor air passing through a dry side of a desiccant wheel to transfer moisture from the air to desiccant material, and then passing heated air through a wet side, where the wheel has rotated, to remove the moisture so it can be discharged somehow. Typically, outdoor air is heated and passed through the desiccant wheel, and the air leaving the desiccant wheel is discharged back into the outside environment. Traditional desiccant-based systems, i.e., “ventilation-cycle” systems, have a fairly low cooling and dehumidification efficiency, which may be between only about 0.6 COP. It is desired to raise this efficiency, and if possible to achieve 1.0 COP or higher.